The present invention relates to a spherical member polishing apparatus, and more particularly to a spherical member polishing apparatus for polishing the surfaces of spherical members to be worked so as to realize perfect sphericity (hereinafter, such spherical members to be worked are referred to as merely "spherical members").
As shown in FIG. 10, a conventional spherical member polishing apparatus includes a storage 52 for storing a plurality of spherical members 51, a rotating disk 53 which is tilted at a predetermined angle .alpha. with respect to the storage 52, and a fixed disk 54 which is disposed in opposition to the rotating disk 53 with a predetermined clearance therebetween (for example, see Unexamined Japanese Patent Publication No. HEI. 5-57602).
In the spherical member polishing apparatus, the spherical members 51 which are stored in the storage 52 are supplied between the rotating disk 53 and the fixed disk 54 via a spherical member loading chute 55. During the one-round travel of the spherical members 51 between the rotating disk 53 and the fixed disk 54 in the circumferential direction, the spherical members 51 are pressurized and polished between the disks 53 and 54, and then discharged via a spherical member discharging chute 56 so as to be recovered into the storage 52.
It is also known in the background art for the other conventional apparatus of a type in which both the rotating disk 53 and the fixed disk 54 are made of hard cast iron, and unhardened spherical members are polished without using abrasive grains, and that in which the rotating disk 53 is made of a grindstone and the fixed disk 54 is made of cast iron so as to polish the spherical members 51 after hardening.
In the conventional spherical member polishing apparatus, as shown in FIG. 11A, the fixed disk 54 includes a plurality of grooves 57a, 57b, 57c which are concentrically formed on the disk, and working-fluid feed pipes 58a and 58b each having an open end are disposed above the fixed disk 54 and in the vicinity of the spherical member loading chute 55. A predetermined amount of working fluid is supplied between the disks 53 and 54 from a working-fluid supplying apparatus 59 shown in FIG. 11B. Specifically, the working-fluid supplying apparatus includes a tank 61 for storing working fluid 60, the working-fluid feed pipes 58a and 58b for supplying the working fluid 60 between the disks 53 and 54, a hydraulic pump 62 interposed in the working-fluid feed pipes 58a and 58b, and a recovering unit 63 for recovering the working fluid 60 discharged from the working-fluid feed pipes 58a and 58b into the tank 61. The working fluid 60 supplied between the disks 53 and 54 applies a cooling function to the spherical members 51 which generate heat due to the frictional heat caused by roll polishing, and is then recovered into the tank 61 via the recovering unit 63.
As another polishing method which uses a spherical member polishing apparatus including the above-mentioned working-fluid supplying apparatus 59, it is also known in that free abrasive grains are suspended in the tank 60, and the free abrasive grains are made to be accompanied with the working fluid 60. Thus, the free abrasive grains are supplied between the disks 53 and 54, so as to polish the spherical members 51.
As described above, in the conventional spherical member polishing apparatus, when the spherical members 51 which are stored in the storage 52 are introduced between the two disks 53 and 54, the spherical members roll and travel first downwardly, and then upwardly against gravity. Thereafter, the spherical members roll and travel downwardly again, so as to be recovered in the storage 52 through the spherical member discharging chute 56. However, since the rotating disk 53 and the fixed disk 54 are tilted as shown in FIG. 10, the working fluid 60 tends to accumulate in the lower portion.
In addition, in the spherical member polishing apparatus, the lower side is open. Therefore, if the working fluid 60 is supplied in the vicinity of the spherical member loading chute 55 or from above of the fixed disk 54, then the working fluid 60 may leak out from the lower portion, or the spherical members 51 may roll and travel upwardly with a reduced amount of working fluid 60. This results in a drawback in that the working fluid 60 cannot be effectively and sufficiently supplied to all points of working spherical members between the two disks 53 and 54.
That is, in the above-described spherical member polishing apparatus, particularly in the case where a plurality of (e.g., 20 or more) grooves 57 are formed on the fixed disk 54, and a large amount of spherical members 51 are polished at one time, for example, in the case where 1,000 spherical members are simultaneously polished, there exist 2,000 to 3,000 working points. However, the working fluid 60 cannot be distributed in the grooves 57 uniformly. This causes a drawback in that the working fluid 60 cannot be effectively and sufficiently supplied to all the working points. Even in the case where the temperature of the working fluid exhibits an average temperature rise of about 50.degree. to 70.degree. C., an extraordinary high temperature is locally realized in some of, for example, 1,000 spherical members which roll between the two disks 53 and 54, because of the shortage of the working fluid 60. This results in such problems that the quality of metallic structure of the spherical members 51 is partly deteriorated so that the surface hardness is lowered.
In addition, in the case where the polishing is performed with using a grindstone as the rotating disk 53, there arise problems in that a long time is required to conform the size and shape of the groove 57 to those of the spherical members 51, because of the high hardness of the grindstone, and that it is difficult to appropriately control the sharpness of the grindstone during the polishing process.
Also in the case where the polishing is performed with using free abrasive grains, the working fluid containing the abrasive grains is not uniformly supplied into the plurality of concentric grooves, so that some of the spherical members 51 are polished with high precision and some are not sufficiently polished. This causes such drawbacks as an error in size and a variation of polishing precision. As a result, there exists a problem in that a fine finishing process is necessary to perform as a next process using working fluid which does not contain abrasive grains, thereby improving the size precision of the spherical members 51 and the gloss of the surface.
As described above, the conventional spherical member polishing apparatus is required to appropriately recover the supplied working fluid in order to maintain a smooth supply of a necessary and sufficient amount of working fluid.